The Mayo TD, Ms Beverley Cooper-Flynn, voted with the Government shortly after losing the Fianna Fail whip at its parliamentary party meeting.
The Government defeated a Labour party private member's motion, calling for radical reform of the Garda, by 72 votes to 65.
Earlier, the Labour leader, Mr Ruairi Quinn, said that members of the Garda should have the right to join a trade union.
"Times have changed, and it is time to change with them," he said.